Windshield wiping system manufacturing method

ABSTRACT

This invention relates to windshield wiper system and method which utilizes a flexible member to account for compression loads in excess of a predetermined load, such as 30 percent, greater than a maximum load for the flexible member. The system utilizes a flexible pultruded composite material having a relatively low modulus of elasticity, yet relatively high elongation characteristics. The flexible arm bends to facilitate preventing damage to components in the wiper system when a compressive load applied to the flexible member is in excess of the predetermined load.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a windshield wiper system and, more particularly, to a windshield wiper system which utilizes at least one flexible member which bends or flexes to compensate for compression loads in excess of a predetermined load.

[0003] 2. Description of the Related Art

[0004] In the field of windshield wiper systems, wiper arms having wiper blades thereon are driven from a park position, where the blades are often situated at either the bottom of or below a windshield of a vehicle, through an inwipe position, to an outwipe position. During normal wiping operations, the blades oscillate between the inwipe and outwipe positions to clean the windshield of debris or particles, such as ice, snow or other debris. It is not uncommon that snow or ice can accumulate on the windshield and prevent the wiper blades from, for example, fully retracting from the inwipe position to the park position when a user actuates a wiper switch to an off position.

[0005] When the debris blocks the wiper arms and blades, a considerable amount of stress is imparted on the wiper linkage and drive motor which drives the blades. For example, a motor drive link, which couples the drive shaft of the motor to the drive linkage which drives the wiper arms, often experiences a compressive force. The linkage members of the wiper systems have in the past been stiffened to reduce expansion and shrinkage in order to avoid changing the wipe pattern requirements for the vehicles. However, in freezing, snowy weather, the snow and ice packs at the bottom of the windshield causes a restriction in the movement in the wiper arm and blade. Because of the rigidity of the motor drive link, the housing which houses the drive gears of the drive motor may crack or break. It has also been experienced that one or more drive plates which directly or indirectly couple the drive link to other linkage have been known to fracture or crack.

[0006] U.S. Pat. Nos. 6,148,470 and 6,381,800 illustrate a composite arm, which are incorporated herein by reference and made a part hereof. Benefits of those inventions are taught in the article “A Novel Use of a Composite Material to Limit the Loads in Windshield Wiper Systems”, Penrod, et al., Copyright 2001 Society of Automotive Engineers, Inc., which is incorporated herein by reference and made a part hereof.

[0007] Accordingly, what is needed is a simple, yet effective, linkage system which utilizes one or more linkage arms having a relatively low modulus of elasticity with relatively high elongation and fatigue properties to facilitate avoiding the problems of the past.

SUMMARY OF THE INVENTION

[0008] In one aspect, this invention comprises a method of making a windshield wiper arm comprising the steps of pultruding a fiberglass material to define a flexible arm that buckles elastically under an axially directed compressive load greater than a predetermined buckling load and exhibits a relatively stiff response to a compressive load below said predetermined buckling load, providing a plurality of surface grooves into said flexible arm and overmolding a socket against said surface grooves.

[0009] Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

[0010]FIG. 1 is a general schematic view of a wiper blade drive and linking system in accordance with one embodiment of the invention;

[0011] FIGS. 2A-2D are illustrations of the wiper blade assembly of FIG. 1 as it is driven from an outwipe position towards inwipe and park positions;

[0012]FIG. 3 is a perspective view of a flexible member in accordance with one embodiment of the invention;

[0013]FIG. 4 is a front view of the flexible member shown in FIG. 3;

[0014]FIG. 5 is a plan view of the flexible member shown in FIG. 3;

[0015]FIG. 6 is a fragmentary sectional view of an end cap situated on the flexible member;

[0016]FIG. 7 is a view similar to FIG. 6 showing a plurality of shear areas to enable the cap to separate from the flexible member when a shear stress exceeds a predetermined amount;

[0017]FIG. 8A is a sectional view taken along the line 8A-8A in FIG. 6;

[0018]FIG. 8B is a sectional view similar to FIG. 8A showing a flexible member with rounded corners;

[0019]FIG. 9 is graphical representation of a relationship between a compressive load for the flexible member relative to the length of the member as it shortens and flexes when the compression load exceeds a predetermined amount;

[0020]FIG. 10 is an illustration of another flexible member in accordance with another embodiment of the invention;

[0021]FIG. 11 is a illustration of the flexible member shown in FIG. 10 showing a shortened length L4;

[0022]FIG. 12 is a sectional view taken along the line 12-12 in FIG. 10;

[0023]FIG. 13 is a sectional view taken along the line 13-13 in FIG. 11;

[0024]FIG. 14 is a detailed drawing of a flexible arm;

[0025]FIGS. 15A and 15B are drawings of first and second ends respectively of a flexible arm;

[0026]FIG. 16 is a drawing of a flexible arm looking in the direction 16-16 of FIG. 14;

[0027]FIG. 17 is a side view of a composite link socket attachment;

[0028]FIG. 18 is a plan view of a composite link socket attachment;

[0029]FIG. 19 is a perspective view of another embodiment of the invention;

[0030]FIG. 20A and FIG. 20B illustrate another embodiment of the invention;

[0031]FIGS. 21A and 21B illustrate load characteristics of the invention;

[0032]FIG. 22 is a view illustrating another test;

[0033]FIG. 23 is a graph illustrating various features of the invention; and

[0034]FIG. 24 is another graph illustrating further load characteristics of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring now to FIGS. 1 and 2A-2D, a windshield wiper system 10 is shown comprising a first wiper 12 and a second wiper 14 for wiping a windshield 16. The wiper 12 comprises a wiper arm 12 a and blade 12 b, and wiper 14 comprises a wiper arm 14 a and blade 14 b.

[0036] The wiper system 10 further comprises a windshield wiper drive linkage or linking means 18 comprising a first link arm 18 on which a drive motor 20 is fastened thereto by conventional means, such as a weld, nut and bolt, or the like. Notice that the frame link 18 comprises a first pivot housing 21 and a second pivot housing 22 which is secured thereto. The housings 21 and 22 comprise a first rotatable pivot housing shaft 21 a and a second rotatable pivot housing shaft 22 a which are drivingly coupled to wiper arms 12 a and 14 a (shown in phantom in FIG. 1), respectively.

[0037] The first rotatable pivot housing shafts 21 a is coupled to a first end 24 a of a drive plate 24. Likewise, the pivot housing shaft 22 a is secured to a first end 26 a of a second drive plate 26, as best illustrated in FIG. 1. An operating or “slave” link 23 couples a second end 24 b of first drive plate 24 to a second end 26 b of second drive plate 26 such that the drive plates 24 and 26 operate synchronously to rotatably drive the pivot housing shafts 21 a and 22 a in the direction of arrow A, thereby driving the wiper blades 12 b and 14 b.

[0038] The linkage or linking means 18 further comprises a motor drive link or flexible arm 28 having a first end 28 a coupled to the second end 24 b of the drive plate 24. The motor drive link or flexible arm 28 further comprises a second end 28 b which is coupled to an output shaft 20 a of motor 20 via a crank arm 30. In this regard, the crank arm 30 comprises a crank arm ball (not shown) and the drive plate 24 comprises a drive plate ball (not shown).

[0039] The arm 28 comprises an elongated rectangular member 29 (FIGS. 3-5) comprising a socket 32 and socket 34 which are over-molded thereon. As best illustrated in FIGS. 3-6, the first end 28 a of motor drive link or flexible arm 28 comprises the socket 32 for mounting onto the drive plate ball (not shown) on drive plates 24, and second end 28 b of motor drive link or flexible arm 28 comprises the socket 34 for receiving crank arm ball (not shown) on crank arm 30. As best illustrated in FIGS. 3-7, the first and second ends 28 a and 28 b comprise the sockets 32 and 34, respectively. Notice that socket 32 (FIG. 6) defines a socket area 40, respectively. It has been found that it is desirable to align the centerline CL (FIG. 5) with the axis of shafts 20 a, 22 a and 24 a when the wipers 12 and 14 are in the park position.

[0040] As best illustrated in FIGS. 2A-2C and 3, flexible arm 28 defines a length L1, which in the embodiment being described is in excess of 250 mm. During a fatigue condition, when the compressive load applied to the arm 28 exceeds a predetermined load (such as at least 30 percent of a maximum working load of flexible member 28 as defined below), the flexible arm 28 begins to flex or bend. This causes the flexible arm 28 to shorten to a length L2, illustrated in FIG. 2D, and this length L2 is shorter than length L1. As illustrated in the graphs shown in FIG. 9 which are referred to and described later herein, the compressive load remains substantially constant as the flexible arm 28 continues to bend or flex and shorten for at least 5 mm after the compressive load achieves the predetermined load.

[0041] As illustrated in FIGS. 3-5, the flexible arm 28 is preferably made from a composite material of the type described later herein relative to Table 1. As best illustrated in FIG. 8A, the flexible arm 28 is generally rectangular in cross-section and is generally elongated (FIGS. 3-5). It should be appreciated that the member 28 could be elliptical, circular or of some other geometry as desired. In the embodiment being described, the length L1 (FIGS. 2A and 3) of flexible arm 28 is on the order of at least 250 mm, but it could be any suitable length depending on the application.

[0042]FIG. 7 illustrates another embodiment of the invention where the flexible member 28 may be provided with sockets 32 and 34 with shear relief areas 50 and 52 which enable the end caps 32 and 34 to shear away or separate from member 29 when a predetermined stress is applied to the flexible member 28. Preferably, the predetermined stress is selected to be just slightly below a break point or maximum load of the member 29 so that, when the member 29 is about to reach its break point, one or more of the sockets 32 or 34 are permitted to shear and separate themselves from member 29 to avoid breakage. As illustrated in FIG. 7, line C defines a shear plane A_(S)=LW and a minimal cross section AC=HW, as shown by line D in FIG. 7. The shear stress along shear plane should not exceed the shearing strength which is defined as follows:

T=P/A _(S) =P/LW≦T _(y) where:

[0043] A_(S)=LW

[0044] L=a length of shear plane (line C);

[0045] W=a width of member 28;

[0046] P=tensile load on member 28 as measured experimentally;

[0047] T=shear stress of member 28; and

[0048] T_(y)=yield shear stress of member 28.

[0049] A tensile stress on the minimum cross section should not exceed a yield stress as follows:

S=P/A _(C) =P/HW≦S _(y)

[0050] Where:

[0051] S=a tensile stress of member 28;

[0052] S_(y)=a yield stress of member 28;

[0053] P=a tensile load on member 28 as measured experimentally;

[0054] H=a height of member 28; and

[0055] W=a width of member 28.

[0056] The general operation of the linkage 18 will now be described relative to FIGS. 1 and 2A-2D. When a user actuates a wiper switch (not shown) the drive motor 20 is energized to cause the wipers to move from a park position (PP) through an inwipe position (IWP) towards an outwipe position (OWP), back to the inwipe position and so on. When the user turns the switch to an off position (not shown), the drive motor 20 drives the crank arm 30 to drive the motor drive link or flexible arm 28 to attempt to drive wipers 12 and 14 from the inwipe position to the park position. The motor 20 rotatably drives crank arm 30 which, in turn, drives the motor drive link or flexible arm 28 to drive the second end 24 b of drive plate 24 in the direction of arrow B in FIG. 1. The operating link 23 responds by directly driving second end 26 b of drive plate 26. The movement of drive plates 24 and 26, in turn, rotatably drive the pivot housing shafts 21 a and 22 a, respectively, to drive the first and second wipers 12 and 14 across the face of windshield 16 in response to rotation of the motor drive shaft 20 a.

[0057] As best illustrated in the FIGS. 2C and 2D, an excessive load condition may occur when snow, ice or some other material or condition (illustrated as 49 in FIGS. 2C and 2D) prevents the wiper blades from moving, for example, from the inwipe position to the park position. However, the motor 20 continues to drive the motor drive link or flexible arm 28. Consequently, a compressive force or load is applied to the arm 28. The flexible arm 28 bends or flexes to facilitate preventing damage to the various components in the wiper system 10 when the load applied to the flexible arm 28 exceeds a predetermined load described later herein. Thus, it should be appreciated, that the flexible arm 28 flexes to accommodate the compressive force or load mentioned earlier when the compressive force or load exceeds the predetermined load.

[0058] In the embodiment being described, it was determined empirically that, when the predetermined load was established is at least 130 percent or more of a maximum normal running load, the arm 28 remained rigid enough to handle the normal wiping, yet flexible enough to bend during fatigue conditions. Thus, when the predetermined load exceeds about 130 percent of the maximum normal running load for the flexible arm 28, the wiper system 10 was able to operate with maximum efficiency, while protecting the components of the system 10. In the embodiment described, the predetermined load is defined as follows:

P _(CR) =KE=1.3 P _(link)

[0059] where:

[0060] P_(CR)=the predetermined load;

[0061] P_(LINK)=a maximum normal running load for a comparably-sized steel or rigid link which does not flex;

[0062] K is a coefficient given by the relation: $K = \frac{\pi^{2}I}{L^{2}}$

[0063] E is the flexural modulus (MPa);

[0064] I is a moment of inertia in mm⁴; and

[0065] L is a length (mm) of flexible arm 28.

[0066] If the cross-sectional shape of member 28 is rounded on its edges as shown in FIG. 8B, then the formula for the area moment of inertia (I) is calculated using the following equation: $I = {{\frac{1}{12}{W\left( {h - {2r}} \right)}^{3}} + {\frac{1}{6}\left( {b - {2r}} \right)} + {\frac{1}{2}{r\left( {h - r} \right)}^{2}\left( {b - {2r}} \right)} + {\frac{1}{4}\left\lbrack {r + \left( {h - {2r}} \right)^{2}} \right\rbrack}}$

[0067] where W, H and R are width, height and fillet radius, respectively, of the cross-section of member 28 shown in FIG. 8B.

[0068] Eight samples of composite material with dimensions as shown in Table 1 below were made and tested using an Instron testing machine. The load and displacement were recorded and the testing results are shown in Table 1 and in the graph illustrated in FIG. 9.

[0069] As illustrated in Table 1, the four different composite materials included a molded glass laminate provided by Red Seal Electric Company of Cleveland, Ohio; a molded epoxy resin provided by International Paper of Hampton, S.C.; a protruded polyester with oriented glass fibers provided by National Composite Center of Dayton, Ohio; and a protruded polyester with unidirectional glass fibers provided by Polygon Company of Walkerton, Ind.

[0070] It should be apparent from the Table 1 that the actual loads (P_(cnt-Exp).) compared vary favorably to theoretical loads (P_(cnt-Theory)). TABLE I L1 (mm) b (mm) h (mm) Pcrit - Pcrit - Material (FIG. 3) (FIG. 4) (FIG. 8) Exp. (N) Theory (N) 1. Glastic Laminate 1a. 253 12.7 3.3 61.71 68.74 1b. 253 19.09 3.3 94.96 103.33 1c. 253 25.32 3.3 131.91 137.05 2. Epoxy Resin (IP) 2a. 253 12.7 3.18 106.23 97.69 2b. 253 19.09 3.18 206.52 146.85 2c. 253 25.32 3.18 290.02 238.47 3. Polyester 300 20 3.4 190.02 238.47 (NCC) 4. Fiberglass 305 31.7 2.42 237.98 219.10

[0071]FIG. 9 graphically illustrates the Instron testing machine results. Notice that, as the load on compressive arm 18 increased to in excess of 300 Newton, the flexible arm 18 began to bend or flex (as shown in FIG. 2D), thereby causing the load to be distributed across the flexible member 28. Notice that the load remains substantially constant even while the motor 20 (FIG. 1) continues to apply torque to the flexible arm 28.

[0072] FIGS. 10-13 illustrate another embodiment of the invention with like parts being identified with the same part numbers, except that a “prime” mark (“′”) has been added thereto. In this embodiment, the flexible arm 28′ has a generally circular cross-section (as shown in FIG. 13) and comprises a plurality of areas of flex 62′ at areas where the flexible member 28′ defines an oval shape in cross section, as shown in FIG. 12. The points of weakness permit the flexible member 28′ to flex at the areas 62′ when the compressive load exceeds the predetermined load, such as 30 percent higher than a maximum working load of the flexible member 28′. Notice that the flexible member 28′ defines a length L3 (FIG. 10) which is greater than the length L4 shown in FIG. 11. It has been found that the difference between the length L3 and length L4, as well as the difference between length L1 and length L2 referred to in the embodiment described above, is directly proportional to the arcuate distance the drive motor 20 continues to drive the drive plate 24 (FIG. 1).

[0073] An ideal flexible member 28 would be perfectly rigid up to a predetermined load and perfectly elastic thereafter. Such a flexible member would have the stiffness necessary in excellent wipe pattern control, while yet limiting the peak loading of the system by elastic buckling at a predetermined yield load. It has been found that a composite link constructed as hereinafter described, provides a flexible member 28 which practically achieves such an operation. Post-buckling behavior of such a flexible member has been found to be very nearly rigid/perfectly plastic in nature. Preferably, flexible member 28 is pultruded from a composite material offering tremendous strain at fracture, allowing the member to undergo appreciable axial compression. For comparison purposes, the composite material is capable of 2.6% strain at fracture whereas 7000 series aluminum is 0.7% at yield, 1080 spring steel is 0.3% at yield, and 1009 CQ steel is 0.1% at yield.

[0074] When wiper system encounters a restriction in the wipe pattern, as illustrated in FIG. 2C, tremendous loads are generated. A composite link provides a solution to this problem. After the restriction has been encountered and the system loading has achieved a prescribed level, the composite link will buckle and become extremely compliant. FIG. 2D depicts this situation. Once the crank arm sweeps through the portion of the pattern that is restricted and the load diminishes, the composite link will unload and revert back to the unbuckled shape. The composite link has the added benefit of mass reduction since a composite link has only about 25% of the weight of its steel counterpart.

[0075] One of the problems in manufacturing a composite link assembly 28 arises in the attachment of sockets 32, 34. Testing results have shown that there is very little bonding strength if the sockets are directly overmolded onto smooth composite links. Therefore, the ends of the composite link bars have to be treated to provide enough bonding strength with the sockets and to avoid damaging the integrity of the resin-fiberglass structure. The following processes have been investigated:

[0076] A. Mechanical Interlock

[0077] grooves top-bottom

[0078] grooves side-side vertical

[0079] grooves side-side horizontal

[0080] grooves side-side at neutral axis

[0081] Description of the Process

[0082] Machining of the cross grooves and the edge grooves requires basically the same machine. The only difference is in the size of the fixture system. The preferred grooving machine is a dedicated milling machine with multiple diamond saws. The parts are loaded on a feeding system that holds the parts laying close to each other guides them under the multiple fixed saws. Since the saws are under and above the parts, both ends and both sides are done at the same time. The cycle time of this process is quite short because the process is running continuously and one operator can take care of several machines. This system can easily be used also to cut the parts at the length with the tolerance desired. For the machining of the axial grooves, the saws have to move with a vertical motion (down and back up) and the feeding system has to be indexed. This system is much more complicated than the one first described above one, and the cycle time is longer, because the system is not really continuous. Both sides and both ends can also be done at the same time with this configuration. This system can be used to cut at length the pultruded parts with the required accuracy.

[0083] B. Abrasive Processing

[0084] grooves top-bottom

[0085] grooves side-side vertical

[0086] grooves side-side horizontal

[0087] grooves side-side at neutral axis

[0088] Description of the Process:

[0089] This is a grit blasting process wherein a small gun creates a stream of pressurized air for blasting an abrasive powder against a work surface. It requires an exhaust system for removal of the dust. The abrasive powder used for this application is aluminum oxide. The grit blast facility uses a feeding system (conveyor) for feeding the parts into the grit blasting machine. The links (single file) are fed past four pressure guns to perform the specific notch cutting operation. Both sides and both ends are done at the same time thanks to the four guns.

[0090] Process Parameters:

[0091] Airpressure: 50 PSI

[0092] Air consumption: 200 SCFM

[0093] Material Specification

[0094] Abrasive: aluminum oxide powder is recycled and runs in a closed loop, only 2% of the powder is lost during each shot.

[0095] Characteristics of the process—Flexible, but noisy. Tools wear rapidly and make lot of dust.

[0096] C-Laser Processing

[0097] grooves top-bottom

[0098] grooves side-side vertical

[0099] grooves side-side horizontal

[0100] grooves side-side at neutral axis

[0101] Roughens the link surface by burning the resin and exposing glass fiber

[0102] Description of the Process:

[0103] The system used to burn or cut the grooves in the composite link is a laser marking system. The laser is an EO Q-switched Nd: YAG operating in the second harmonic (532 nm). This kind of laser produces pulses approximately 15 ns wide and combines both thermal and ablative properties. The process is accomplished by putting the composite link beneath the beam of a laser that has been defocussed to reduce the power density. Nitrogen gas is blown just on the surface of the link to clear the debris. Only one side and both ends of the link can be done at the same time so the link has to be turned around by an operator. The links are put on a conveyor (feeding system) that is indexed after each cycle of the laser so that two ends of two links are in the action window of the laser. The system has also a cooling station and an exhaust system for the fumes.

[0104] Process Parameters:

[0105] Nitrogen pressure: 30 PSI

[0106] Vertical position precision needed: +/−{fraction (1/1000)} inch

[0107] Frequency: 0 to 50 Hz

[0108] Material Specification:

[0109] Cleaning gas: nitrogen, argon but not air (could burn)

[0110] Crystal: Nd YAG

[0111] Characteristics of the Process

[0112] No noise

[0113] No wear of the tools

[0114] Very flexible but gas must be handled: argon or nitrogen

[0115] D-Plasma

[0116] Description of the Process:

[0117] The plasma burning station is composed of a power supply (same kind as the one for the plasma welding), two plasma torches and two motion systems. The two torches (one above and one under the composite links) are moved close to the still link by the motion systems controlled by a control station. The composite links are still and the operator puts them in the machine per batch. The plasma beam is a non-transferred beam (because the composite is not conductive) and is created by the electric power and argon gas that also protects the electrodes from oxidation. The beam is 1 inch above the surface of the composite so that it doesn't touch the link but creates such a high temperature that the resin of the composite burns but not the fibers. The system has also an exhaust system for the fumes and at least one operator for three plasma machines. The process has no noise and no wear on tools and is very flexible, but cannot be used to do grooves. This approach requires the use and handling of argon gas.

[0118] Extreme caution should be used if the width, depth, spacing or number of grooves is changed or if the thickness of the pultruded rod is reduced below about 5.20 mm. When the member is buckled, the composite has a tendency to delaminate, a phenomenon which manifests itself by the appearance of small cracks at the roots of the grooves. Extensive development testing was completed in order to find a groove configuration that would meet the strength requirement when the link was in tension, yet not be subject to delamination at peak mid-span stress levels up to 690 MPa (100 ksi) that can occur when the composite link 28 is buckled. FIGS. 14, 15A, 15B and 16, particularly reference numeral 104 of FIG. 15A, illustrate the recommended top and bottom groove geometry. Note the two sets of grooves 104 a and 104 b (FIG. 15A). Note that the grooves 104 extend across the entire length W (FIG. 8B), but they could extend only part way across the width if desired. Also, they are shown to be linear, but they could comprise another shape, such as curved. FIGS. 17 and 18 show the side-by-side grooves 106 at the neutral axis of the link-bending plane. This design can reduce the peak bending stress where the glass fibers are removed, so that weakness is minimized. Finally, FIGS. 19, 20A and 20B show various alternative embodiments of circular and elongated or elliptic openings 108, 110 and 112, respectively, that may be used to provide the interlocking joint when one of the sockets 32 or 34 is overmolded thereon.

[0119] Special attention must be paid to the resin flow during the socket overmolding process. It is important to ensure that the Nylon material completely fill the grooves machined onto the composite rod. Table II presents a design of experiment (DOE) matrix comparing thirty-two configurations of the invention. A C D E e Grooves Surface Finish Socket Material Attachment Method Pultrusion Priming 1 smooth smooth nylon insert mold pultrusion w/o at-prime 2 smooth ground axial fiber exposure acetal insert mold pultrusion w/ at-prime 3 smooth plasma axial fiber exposure nylon adhesive assy w/o surface primer pultrusion w/o at-prime 4 smooth laser axial fiber exposure acetal adhesive assy w/ surface primer pultrusion w/ at-prime 5 machined axial grooves smooth nylon insert mold pultrusion w/ at-prime 6 machined axial grooves ground axial fiber exposure acetal insert mold pultrusion w/o at-prime 7 machined axial grooves plasma axial fiber exposure nylon adhesive assy w/ surface primer pultrusion w/ at-prime 8 machined axial grooves laser axial fiber exposure acetal adhesive assy w/o surface primer pultrusion w/o at-prime 9 machined cross grooves smooth acetal adhesive assy w/o surface primer pultrusion w/ at-prime 10 machined cross grooves ground axial fiber exposure nylon adhesive assy w/ surface primer pultrusion w/o at-prime 11 machined cross grooves plasma axial fiber exposure acetal insert mold pultrusion w/ at-prime 12 machined cross grooves laser axial fiber exposure nylon insert mold pultrusion w/o at-prime 13 machined edge grooves smooth acetal adhesive assy w/ surface primer pultrusion w/o at-prime 14 machined edge grooves ground axial fiber exposure nylon adhesive assy w/o surface primer pultrusion w/ at-prime 15 machines edge grooves plasma axial fiber exposure acetal insert mold pultrusion w/o at-prime 16 machined edge grooves laser axial fiber exposure nylon insert mold pultrusion w/ at-prime 17 laser axial grooves smooth acetal insert mold pultrusion w/ at-prime 18 laser axial grooves ground axial fiber exposure nylon insert mold pultrusion w/o at-prime 19 laser axial grooves plasma axial fiber exposure acetal adhesive assy w/o surface primer pultrusion w/ at-prime 20 laser axial grooves laser axial fiber exposure nylon adhesive assy w/ surface primer pultrusion w/o at-prime 21 laser cross grooves smooth acetal insert mold pultrusion w/o at-prime 22 laser cross grooves ground axial fiber exposure nylon insert mold pultrusion w/ at-prime 23 laser cross grooves plasma axial fiber exposure acetal adhesive assy w/ surface primer pultrusion w/o at-prime 24 laser cross grooves laser axial fiber exposure nylon adhesive assy w/o surface primer pultrusion w/ at-prime 25 grit blast cross grooves smooth nylon adhesive assy w/o surface primer pultrusion w/o at-prime 26 grit blast cross grooves ground axial fiber exposure acetal adhesive assy w/ surface primer pultrusion w/ at-prime 27 grit blast cross grooves plasma axial fiber exposure nylon insert mold pultrusion w/o at-prime 28 grit blast cross grooves laser axial fiber exposure acetal insert mold pultrusion w/ at-prime 29 ground cross grooves smooth nylon adhesive assy w/ surface primer pultrusion w/ at-prime 30 ground cross grooves ground axial fiber exposure acetal adhesive assy w/o surface primer pultrusion w/o at-prime 31 ground cross grooves plasma axial fiber exposure nylon insert mold pultrusion w/ at-prime 32 ground cross grooves laser axial fiber exposure acetal insert mold pultrusion w/o at-prime

[0120] It should be appreciated that although the grooves are shown as illustrated in the figures, other groove configurations or arrangement of the grooves could be provided without departing from the scope of the invention. For example, it has been found that providing a different number of grooves on one surface, such as grooves 104 b on surface 28A1 in FIG. 15A and three grooves 104 on the opposite surface, such as grooves 104 a on surface 28A2 in FIG. 15A, with the grooves 104 a and 104 b being arranged in a staggered configuration relative to each other has been found to be the preferred configuration.

[0121] Table III represents further DOE relative to socket attachment for eighteen samples. Note that each sample had a predetermined surface finish (smooth, abrasive-fine, abrasive-coarse, chemically etched, laser etched); machine grooves (smooth, which means no grooves; top and bottom grooves as shown in FIG. 15A; and side-by-side grooves, as illustrated in FIG. 17); socket material from which the link 28 was made; the method by which the sockets 32 and 34 were mounted onto the ends 28A and 28B of arm 28; and protrusions having varying degrees of modulus. In the embodiment being described, the low modulus was provided to be about 40 percent glass filled, moderate modulus was about 50 percent glass filled and high modulus was provided to be about 60 percent glass filled in the embodiment being described. TABLE III DOE of Socket Attachment 1&2 3 4 5 6 A B D E F Surface finish Machined grooves Socket material Attachment/adhesives Pultrusions 1 smooth smooth nylon insert mold/hot curing low modulus 2 smooth top-bottom acetal #1 mech attach/chem cure moderate modulus 3 smooth side-side acetal #2 insert mold/no adhesive high modulus 4 abrasive-fine smooth nylon mech attach/chem cure moderate modulus 5 abrasive-fine top-bottom acetal #1 insert mold/no adhesive high modulus 6 abrasive-fine side-side acetal #2 insert mold/hot curing low modulus 7 abrasive-coarse smooth acetal #1 insert mold/hot curing high modulus 8 abrasive-coarse top-bottom acetal #2 mech attach/chem cure low modulus 9 abrasive-coarse side-side nylon insert mold/no adhesive moderate modulus 10 chemical etch smooth acetal #2 insert mold/no adhesive moderate modulus 11 chemical etch top-bottom nylon insert mold/hot curing high modulus 12 chemical etch side-side acetal #1 mech attach/chem cure low modulus 13 laser etch #1 smooth acetal #1 insert mold/no adhesive low modulus 14 laser etch #1 top-bottom acetal #2 insert mold/hot curing moderate modulus 15 laser etch #1 side-side nylon mech attach/chem cure high modulus 16 laser etch #2 smooth acetal #2 mech attach/chem cure high modulus 17 laser etch #2 top-bottom nylon insert mold/no adhesive low modulus 18 laser etch #2 side-side acetal #1 insert mold/hot curing moderate modulus

[0122] It should be appreciated that in the embodiment being described, the desired groove size, groove spacing and number of grooves is selected to provide a predetermined configuration that optimized the interlock between the socket, such as socket 32 and the arm 28. The following Table IV illustrates the various combinations of groove size, groove spacing and number of grooves selected. TABLE IV 1 2 3 A B C Groove Size Groove Spacing Number of Grooves 1 small #1 few 2 small #2 moderate 3 small #3 many 4 medium #4 moderate 5 medium #5 many 6 medium #6 few 7 large #7 many 8 large #8 few 9 large #9 moderate

[0123] In the embodiment being described it was determined that the sample number 2 in Table III was preferred. This design was further tested by conducted bearing strength tests (pulling through the ball sockets 32 and 34 using the fixture 116 in FIG. 21B); a joint strength test (using the fixture 110 illustrated in FIG. 21A); a static strength (bearing) test (Table VII); and a spectrum buckling durability test (Table VIII).

[0124] Two unique testing procedures were set up to test the strength of the interlock between the sockets 32 and 34 and the flexible arm 28. FIG. 21A illustrates a testing fixture 110 defining a U-shaped area 112 for receiving a socket 32 and having a wall 110 a having a surface 110 a 1 for engaging an end 32 a 1. It should be appreciated that the wall 110 a comprises a slot 105 substantially corresponding to the dimension H (FIG. 8A) so that it can receive the arm 28. The arm 28 and fixture 110 are moved in the direction of the arrows K and L until of the sockets 32 and/or 34 separate, as illustrated in FIG. 21B. The results of the tests using the sample 2 (Table III) is shown in the following Table V: Tables V and VI Table V A. Bearing Strength Test (pull through ball sockets) Sample Pull Rate Max Load Fail Mode Groove Groove No. (N) Size Spacing (mm) (mm) I 1.0mm/mm 3100.7 upper-joint 0.5 2 2 1.0 mm/mm 2649.4 lower - socket 0.5 2 3 10.0mm/mm 2937.9 upper-socket 0.5 2 410.0 mm/mm 2946.6 upper-joint 0.5 2 510.0 mm/mm 2871.6 lower-joint 0.5 2 Mean Load @Failure 2901.24 Standard Deviation 163.927 Table VI B. Joint Strength Test (using stripping fixture) Sample No. Pull rate Max Fail Mode Groove Size Groove Load (N) Joint (mm) Spacing (mm) Joint 610.0 mm/mm 3940.4 upper 0.5 2 710.0 mm/mm 3902.9 lower 0.5 2 810.0 mm/mm 3724.3 lower 0.5 2 910.0 mm/mm 3878.4 lower 0.5 2 1010.0 mm/mm 3937.4 lower 0.5 2 Mean Load failure 3876.68 Standard Deviation 88.962

[0125] A second bearing strength test was conducted to test the strength of the socket 32 and length 28 and the joints therebetween. In this test, a fixture 116 (FIG. 22) having a ball 118 was provided and inserted into the socket 32 as illustrated FIG. 22. Loads were then applied in the directions of arrows M and N until the socket wall 32 a 2 illustrate the results from the tests conducted. These results for the same sample are shown in Table VI.

[0126] In Table VII, the arm 28 was subject to a static strength test at the loads indicated. Table VII illustrates the shear at the edge 32A1 (FIG. 21A) and the arm 28. For example, note in one test shear did not occur until an elongation of about 3 millimeters, which occurred in one test after applying a maximum load of about 3170 Newtons. TABLE VII CWL Static Strength (Bearing) Test Results Max Elongation Groove Size Groove Spacing Load (N) (mm) Failure Mode (mm) (mm) 3227 3.14 Interface 1.0 3.00 3185 2.99 Interface 1.0 3.00 3170 3.00 Interface 1.0 3.00 3097 2.72 Interface 1.0 3.00 3832 4.27 Interface 0.50 2.00 3787 3.74 Interface 0.50 2.00 3246 3.08 Interface 0.50 2.00 3149 3.07 Interface 0.50 2.00 3187 3.11 Interface 0.50 2.00 3323 3.41 Interface 0.50 2.00 3225 3.22 Interface 0.50 2.00 3379 3.33 Interface 0.50 2.00 3379 3.37 Interface 0.50 2.00 3351 3.34 Interface 0.50 2.00

[0127] Likewise, the following Table VIII illustrates further features of the invention showing various buckling durability tests over a repeated number of cycles and a corresponding failure mode which varied based upon the groove configuration selected. For example, various groove configurations (e.g., 4/3, 4/4, etc.), such as a staggered four on top, three on bottom configuration, were tested at various stress levels as the sockets 32 and 34 were repeatedly brought towards each other. The failure mode experienced resulted in either a delamination where outside layers of the composite material separated or where both delamination or breaking of the arm 28 occurred. Sometimes at the midspan area (i.e., towards the middle of the arm 28 between its ends 28A and 28B where maximum bending stress occurred. TABLE VIII CWL Specimen Buckling Durability Tests Failure modes: Groove Configuration Test Stress (ksi) Test Displ (in) Cycles Failure Mode Groove Size r(mm) Groove Spacing(mm) 4/3 90 0.669 29,457 Delam. 1.00 4.00 4/3 80 0.593 55,000 Both 1.00 4.00 4/3 70 0.422 240,000 Midspan 1.00 4.00 5/4 90 0.669 20,000 Delam 0.50 2.00 5/4 80 0.539 40,722 Both 0.50 2.00 5/4 70 0.422 291,902 Both 0.50 2.00 5/4 80 0.539 40,000 Delam. 0.50 2.00 None 100  0.812 15,000 Midspan None 90 0.669 25,000 Midspan None 80 0.539 100,000 Midspan 4/4 90 0.669 25,000 Midspan 0.50 3.00 4/4 95 0.739 30,000 Midspan 0.50 3.00 4/4 100  0.812 15,000 Midspan 0.50 3.00 4/4 85 0.603 30,000 Midspan 0.50 3.00 4/4 80 0.539 60,000 Midspan 0.50 3.00 4/4 75 0.479 160,000 Midspan 0.50 3.00 4/4 70 0.422 210,000 Midspan 0.50 3.00 4/4 95 0.739 25,000 Midspan 0.50 3.00 4/4 85 0.603 25,000 Midspan 0.50 3.00

[0128] The results in Tables V through VIII illustrate the strength and durability of the interlocking joint provided by the groove design between the sockets 32 and 34 and the arm 28 to which they are over molded. Moreover, the sockets 32 and 34 resisted separation from the ends of the arm 28 both in a static, non bending state as well as in a buckling or bent state during which a fatigued condition on the windshield would normally be occurring.

[0129] While the method herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims. 

What is claimed is:
 1. A method of making a windshield wiper arm comprising the steps of: pultruding a fiberglass material to define a flexible arm that buckles elastically under an axially directed compressive load greater than a predetermined buckling load and exhibits a relatively stiff response to a compressive load below said predetermined buckling load; providing a plurality of surface grooves into said flexible arm; and overmolding a socket against said surface grooves.
 2. The method of claim 1 wherein said plurality of surface grooves include at least one axial groove and at least one cross groove.
 3. The method of claim 1 wherein said cutting step is performed with the aid of a milling machine.
 4. The method of claim 1 wherein said cutting step is performed with the aid of a laser.
 5. The method of claim 1 wherein said cutting step is performed with the aid of a plasma torch.
 6. The method of claim 1 wherein said overmolding step is continued until said plurality of surface grooves are entirely filled by molding material.
 7. The method of claim 1 wherein said overmolding step includes the step of overmolding a socket on each end of said flexible arm.
 8. The method of claim 1 providing said plurality of surface grooves on a first end of said arm and a second end of said arm.
 9. The method of claim 1 wherein said providing step comprises the step of cutting said plurality of surface grooves into said flexible arm.
 10. The method of claim 8 wherein said providing step comprises the step of cutting said plurality of surface grooves into said flexible arm.
 11. The method of claim 10 wherein said plurality of surface grooves include at least one axial groove and at least one cross groove.
 12. The method of claim 10 wherein said cutting step is performed with the aid of a milling machine.
 13. The method of claim 10 wherein said cutting step is performed with the aid of a laser.
 14. The method of claim 10 wherein said cutting step is performed with the aid of a plasma torch.
 15. The method of claim 10 wherein said overmolding step is continued until said plurality of surface grooves are entirely filled by molding material. 